In many situations, it is of critical importance to be able to accurately measure the tension on a rope or cable. For example, in oil drilling applications, a cable may be used to support the weight of the drilling apparatus. Typically, the cable is secured at the top of the drilling rig, and may be connected to the drilling equipment which is lowered into the well shaft to perform the drilling operation. When drilling, it is necessary to monitor the weight borne by the support cable to prevent both slack and overload situations. Accurate cable load measurement is necessary to maintain safe working conditions in the drilling operation, as well as to prevent damage to drilling equipment.
In the prior art, cable tension is often measured by in-line load cell devices equipped with strain gages. Strain gages are typically expensive to manufacture and replace, and may be susceptible to fluctuations due to surrounding physical conditions. In addition, many strain gages are integral to the in-line load cell device, and failure of the gages requires extensive repair or replacement of the entire load cell. This replacement may cause significant downtime and additional expense, as the drilling operation must be stopped to remove the load cell from its position on the cable.
In many applications, such as oil drilling, the weight sensor device is used in harsh conditions. Typically, the weight sensor is exposed to dirt and other debris, as well as fluids such as oils and industrial lubricants. In addition, the sensor may be frequently exposed to high pressure steam used to clean components of the oil derrick. These conditions may contribute to premature failure of the weight sensor device.
Therefore, there is a need for an improved weight sensor device which can accurately measure a cable load under such harsh operating conditions and may be repaired quickly and inexpensively.